Single crystal tungsten penetrator and method of making

ABSTRACT

High density single crystal penetrators are made from tungsten or from alloys containing at least 90% tungsten, and a remainder of essentially tantalum, rhenium, niobium, molybdenum or a mixture thereof. The penetrator will generally be circular in cross-section and have a length to diameter ratio of at least about 10 to 1, with the single crystal body being aligned so the crystalline axis having the [100] orientation is parallel to the longitudinal axis of the penetrator. A penetrator having such desired crystalline characteristics can be formed by CVD about a heated substrate of body-centered cubic crystal material. One particularly efficient process utilizes static CVD in a closed chamber and employs a solid feedstock of polycrystalline tungsten material.

This application is a continuation-in-part of U.S. Ser. No. 10/046,096,filed Jan. 11, 2002, which was a continuation of InternationalApplication No. PCT/US00/19031, filed Jul. 12, 2000, which claimedpriority from U.S. Ser. No. 60/143,827, filed Jul. 13, 1999, thedisclosures of all of which are incorporated herein by reference.

There may be environmental and occupational hazards associated with themanufacture, deployment and use of depleted uranium (DU) as a ballisticpenetrator. It would be desirable to have an alternative, benignmaterial having penetration characteristics at least about equal to DU.

When a penetrator interacts with armor, it generates an aerosol andparticles which are respirable and which may reach the gas exchangeregion of the human lung. In addition, penetrator impact fragments aredeposited into the soil and can eventually find their way into the humanfood chain. DU is known to be toxic to the kidney, and it is alsotheoretically carcinogenic because of its residual radioactivity. Knowntungsten heavy alloys, besides being inferior in penetration performanceversus DU, contain nickel and cobalt alloying constituents that are alsoknown to be toxic.

As a result of the foregoing, the testing of munitions with DUpenetrators is limited to a few testing ranges within the U.S., andessentially, warfighters cannot train with the actual ammunition theywill use in wartime because of the severe restrictions placed ontraining exercises at even these limited testing ranges in the U.S.After DU munitions are used in war (e.g. Desert Storm), a subsequentcleanup effort should be conducted to recover DU from the soil andprevent it from entering a food chain. Stored DU ammunition must becontinuously inspected and accounted for during peacetime, introducing anon-productive accountancy requirement to the U.S. logistics chain.

Attempts have heretofore been made to develop polycrystallinetungsten-based composites and tungsten heavy alloys as replacements forDU. Despite developments that led to some increases in strength andtoughness, the basic penetration performance of these materials did notsignificantly improve and did not approach that of DU. These studiesdemonstrated that penetration performance is not solely a function ofstrength or ductility.

After much research, it is now believed that material flow and failuremechanisms, not strength and ductility, are key properties indetermining penetration performance. As a penetrator strikes armor, ahigh deformation rate in the penetrator causes heat to be generated.Because there is not enough time to conduct/diffuse this heat away fromthe deformation area, thermal softening occurs which overcomes theeffect of previous hardening mechanisms, such as strain hardening. As aresult, gross penetrator deformation occurs in locally softer material,along adiabatic shear bands, and the rapid failure along these adiabaticshear bands allows the penetrator to rapidly shed excess material. Thisrapid, localized deformation allows material to slough off and thusmaintains a small diameter at the penetrator/armor interface. Withoutsuch localized shearing, the penetrator would form a large-diameter,blunt-nosed head that is much less effective. For a given value ofkinetic energy, the small diameter penetrator will need to move lessarmor material, and will penetrate farther, than a larger, blunt-nosedpenetrator.

The deformation behavior of DU follows the adiabatic shear bandphenomenon described above, and the self-sharpening DU penetratorproduces a small diameter hole in the armor. Single crystal unalloyedtungsten is also found to exhibit local deformation behavior, alongcrystalline planes, similar to that of DU. Single crystal unalloyedtungsten, when its [100] axis is parallel to the direction of travel,exhibits penetration capabilities equal to that of DU. Performance inother crystalline orientations, such as [111] or [110], is inferior tothe [100] orientation. However, single crystal unalloyed tungsten has ahigh muzzle-launch failure rate; it appears to lack sufficient strengthand ductility to reliably remain intact after launching.

The following criteria have now been developed by U.S. Army TACOM-ARDECfor screening candidate penetrator materials. If a candidate materialmeets and/or exceeds these screening criteria, it is felt that there isa high assurance that the material will survive muzzle launch. Thesescreening criteria are:

-   -   Ultimate Tensile Strength≧180 ksi;    -   Tensile Yield Strength≧100 ksi; and    -   Elongation≧12%.

It is an object of the present invention to provide high densitypenetrators that will meet the foregoing criteria and to provide methodsfor efficiently and economically fabricating such Penetrator.

SUMMARY OF THE INVENTION

Certain high creep strength, single crystal tungsten alloys have nowbeen developed which have increased strength and ductility compared tothat of unalloyed single crystal tungsten; however, in someapplications, substantially pure single crystal tungsten may suffice.Tensile tests of one such single crystal tungsten alloy produced thefollowing results:

-   -   Ultimate Tensile Strength≧200 ksi;    -   Tensile Yield Strength≧100 ksi; and

Elongation≧20%.

Such single crystal tungsten alloys have sufficient strength andductility to survive muzzle launch and single crystal pure tungstenbodies are also so considered to survive. Such high tungsten alloyscontain at least about 90% tungsten, generally between about 90% andabout 97%, and alloyed with tungsten will be tantalum, rhenium, niobium,molybdenum or a mixture of two or more of these metals. Hereinafter, forthis application, reference to “tungsten” by itself should be understoodto refer to a metal material that is at least about 90% by weighttungsten.

Also provided are methods for economically and efficiently producingsuch high density penetrators using CVD. By using an appropriate singlecrystal substrate and CVD, it has been found that a single crystal bodysuitable for use as a high density penetrator can be fabricated fromtungsten. In addition, a generally closed CVD system is also providedwhich makes very efficient use of raw materials and minimizes thecreation of reaction by-products that would otherwise require processingand/or other clean-up treatment prior to being discarded.

In one particular aspect, the invention provides a high densitypenetrator designed to be propelled from the muzzle of a weapon, whichpenetrator is generally circular in cross-section, has a diameter of atleast 3 mm and a length to diameter ratio of at least about 5 to 1 andcomprises a shaped single-crystal alloy body consisting essentially ofat least 90% tungsten, said single-crystal body being aligned with [100]orientation with respect to its long axis and being encased in a metalor metal alloy material that has a ductility and strength greater thanthe ductility and strength of said single-crystal body, said encasingmaterial surrounding a head end portion of said single-crystal body andat least substantially the entire length thereof.

In another particular aspect, the invention provides a method for makinga single crystal, high density alloy body containing a major amount oftungsten and a minor amount of tantalum, rhenium, niobium and/ormolybdenum as an alloying metal, which body is suitable for use as ahigh density penetrator, said method comprising providing a chambersuitable for carrying out chemical vapor deposition (CVD), locating asingle crystal substrate which is stable at a temperature of at leastabout 800° C. within said chamber, introducing (a) tungsten chloride orfluoride vapor or (b) a vapor mixture of chlorides or fluorides oftungsten and said alloying metal into said CVD chamber, with theoptional inclusion of H₂, and heating said single crystal substrate toat least about 800° so as to cause a single crystal tungsten alloy bodyof desired composition to grow upon the exterior surface of said singlecrystal substrate and create a high-density tungsten alloy body suitablefor use as a penetrator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 are sectional views of high density penetratorsembodying various features of the invention;

FIG. 4 is a schematic view showing the formation of a high densitypenetrator using CVD;

FIG. 5 is a view similar to FIG. 4 showing an alternative CVD processembodying various features of the invention; and

FIG. 6 is a view similar to FIG. 5 showing another alternative CVDprocess embodying various features of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Bodies of single crystal material can be formed from tungsten which willhave characteristics that will meet desired criteria set down by theUnited States Army for high density penetrators that will survive muzzlelaunch from a weapon. These single crystal materials should contain atleast about 90% tungsten, e.g. about 90 to about 100%, preferablycontain between about 91% and about 95% tungsten and more preferablycontain between about 92% and about 94% tungsten, with one preferredalloy containing about 93% tungsten. Tungsten has a body-centered cubiccrystalline structure, and alloying elements, when included, shouldeither have a body-centered cubic crystal structure or a hexagonalclose-packed crystal structure. The remainder of the alloy preferablycontains tantalum, rhenium, niobium, molybdenum or a mixture of two ormore of such metals. Although minor amounts of other elements havingsuch a crystal structure can be tolerated, such presence should beminimized so as not to detract from the desired high density of thebody. Of the candidates for alloying elements, rhenium has aparticularly high density, and tantalum alloys exhibit particularly highstrength. Accordingly, tantalum and rhenium are considered to bepreferred alloying agencies. As an example, one preferred alloy containsabout 93% tungsten and about 7% tantalum. The single crystal body shouldhave a density of at least about 98% of its maximum theoretical density.

The penetrators may have various shapes so long as they are suitable forbeing propelled from the muzzle of a weapon, e.g. canons, machine gunsand the like. They will normally have a fairly high length to diameterratio, and they will usually have either an aerodynamically-shaped heador be embodied within a mass that has such a aerodynamically-shaped headas described hereinafter.

FIG. 1 shows a single penetrator or projectile 11 that is made ofsubstantially homogenous material which is a single crystal tungstenalloy, e.g. 93% W and about 7% Ta. The penetrator 11 has a cylindricalmain body 13 and a generally conical head 15. It should have alength/diameter ratio of at least about 5 to 1, preferably at leastabout 10 to 1 and more preferably at least about 15 to 1. For example, apenetrator of a larger class may be formed of single crystal materialhaving a diameter of about 1 inch and a length from about 14 to 24inches. Smaller size penetrators may have, for example, a diameter of8.31 mm and a length of 96.4 mm or a diameter of 12.68 mm and a lengthof 70.5 mm. The single crystal tungsten alloy is formed such that thebody-centered cubic crystalline structure is oriented so that the [100]crystalline axis is parallel to the axis of the penetrator 11. Suchprojectiles are capable of penetrating the armor of tanks and/orpersonnel carriers.

It has been found that, in some instances, it may be desirable (see FIG.2) to encase a single-crystal body 17 in an exterior shell or sheath 19of a fairly similar dense alloy that has strength and ductility higherthan that of the single crystalline body to create an effectivepenetrator. Examples of suitable materials are those which contain atleast about 90% tungsten and various amounts of nickel, iron and/orcobalt. One that is referred to as WHA contains 93% W, 4.9% Ni and 2.1%Fe; another contains 97.1% W, 1.4% Ni, 0.7% Fe and 0.8% Co. If, forexample, it were desired for such a penetrator to have a diameter ofabout 1 inch, the thickness of the encasing, stronger, more ductile,dense material might be about 0.1 inch (2.5 mm). As illustrated in FIG.2, the encasing sheath 19 could completely cover the single crystal body17 or, if desired, the encasing material could be omitted at the flattail end of the penetrator.

A further alternative example of a penetrator 21 is shown in FIG. 3wherein a plurality of uniformly spaced apart rods 23 of single crystaltungsten alloy material are embedded in a matrix 25 that is formed fromsuch dense more ductile tungsten alloy, such as WHA which was discussedabove. In such an instance, this plurality of single crystal rods 23might be individually about {fraction (1/8)} inch to {fraction (1/4)}inch (about 3 mm to about 6 mm) in diameter, with the conical head endof the penetrator 21 being formed of WHA or the like. For example, apenetrator 21 of this style might include 44 single crystal, highdensity, tungsten alloy rods, each about {fraction (1/4)} inch indiameter and 23 inches in length, uniformly spaced within a cylindricalbody of WHA having a diameter of about 1 inch. Such an arrangement mayhave fabrication advantages particularly when the high density singlecrystal tungsten alloy rods are being grown from fine wire cores.

The single crystal body can be formed using a zone-refining process, asknown in this art, in which an electron beam filament carefully locallyheats a rod to cause localized melting and then recrystallization. Asingle crystal seed is located at the bottom of a polycrystalline rod ofthe desired alloy composition. The electron beam filament initiallyheats and melts the bottom of the polycrystalline rod where there iscontact with the single crystal seed which is oriented with its [100]axis aligned with the long axis of the rod that will constitute thepenetrator. The single crystal structure of the seed and its orientationspreads into the molten zone, transforming that portion of the nowmelted polycrystalline rod into conforming single crystal material. Thefilament slowly travels up the length of the rod, producing a localmolten zone as it travels. This enables the single crystal structure tospread upward, the molten zone transforming the former polycrystallinecrystallography into a single crystal having the desired axialorientation. The resultant single crystal material can then be shaped bygrinding or other machining operations so as to have the desiredpenetrator shape, e.g. a solid cylinder having an external head endtaper as shown in FIG. 1, plus desired grooves and/or threads and thelike.

It has been found that high density single crystal material having adesired crystalline axial orientation can also be formed usingconventional chemical vapor deposition (CVD) methods. As depictedschematically in FIG. 4, a vaporous (gaseous) mixture of WF₆/TaF₅/H₂ orWCl₆/TaCl₅ can be caused to flow over a heated, single-crystal mandrelhaving a body centered cubic crystalline structure (Mo for example), andan alloy of tungsten and tantalum can be deposited which will adopt thesingle crystal structure and the crystalline axial orientation of themandrel/substrate.

Using a standard quartz chamber or enclosure 31, an alloy is depositedfrom a mixture 33, for example, having the appropriate proportions oftungsten fluoride, tantalum fluoride and hydrogen, which may be suppliedthrough an upper entrance 35. By heating a fine wire or thin rod beingused as a substrate 37, a single crystal body 39 is formed at asubstrate temperature of at least about 800 to 900° C. under otherwisestandard CVD operating conditions, i.e. flowing the gaseous mixturedownward through the coating chamber 31 under reasonably high vacuumconditions (e.g. about 1-20 torr) and at a rate of about 1.5 μm to about25 μm per minute. Higher temperatures can be employed and may bepreferred depending upon the diameter of the final product that isdesired as explained hereinafter. The desired single crystal materialgrows uniformly radially outward about the surface of the molybdenumwire substrate. Although other body-centered cubic crystalline materialscan be used as the substrate 37, single crystal molybdenum is fairlyreadily available and is preferred for this reason.

If instead a mixture of tungsten and tantalum chlorides is used togetherwith a higher temperature of about 1200 to about 1300° C. and otherwisestandard CVD conditions, the desired alloy will be readily depositedwithout the inclusion of hydrogen. Thus, the inclusion of hydrogen inthe gaseous mixture is considered to be optional, and therefore only aminor amount or no hydrogen may be included. The unreacted chloridesand/or fluorides along with the HF or Cl₂ reaction products are removedfrom the opposite end 40 of the chamber wherein the coating takes placeand must be appropriately reclaimed or disposed of. By appropriatelyselecting the substrate as a body-centered cubic crystal material withits [100] axis oriented longitudinally, the desired high densitytungsten alloy body 39 having single crystal form and this desiredcrystalline orientation is obtained.

Both of the foregoing methods are fairly expensive to operate, and ithas now been found that a single crystal tungsten alloy material canalso be produced using what is being termed a static CVD system and isschematically shown in the accompanying FIG. 5. In this system, vaporousWF₆/H₂ or WCl₆ reactants are initially supplied to an otherwise closedreaction chamber 41. The illustrated system is adapted to deposit atungsten alloy by positioning a solid feedstock 43 of polycrystallineelemental alloy material within the chamber, preferably in surroundingrelationship to a centrally located single crystal substrate 45. Withinthis closed volume, a partial pressure of H₂ (optional) and, forexample, either (a) WF₆ or WF₆ and TaF₅ or (b) WCl₆ or WCl₆ and TaCl₅vapors are initially provided, as by heating a suitable reservoir 47containing one or more such reactants 48 to about 80 to 200° C. byemploying a suitable heater and optionally adding H₂ (not shown) to thestream which is fed through a valve 50. As previously mentioned, whentungsten chloride is employed, it should not be necessary to addhydrogen although the presence of hydrogen is not felt to detract at allfrom such CVD. Moreover, it may not be necessary to include a minoramount of the halide of the alloying metal in the vaporous atmospherethat is initially supplied, as this small amount of vapor will accountfor only a very minor deposition onto the surface of the heatedsubstrate 45, creating a Cl₂ atmosphere that then reacts with thepolycrystalline alloy feedstock 43 to thereafter create the desiredvaporous alloy composition within the closed chamber 41.

As seen in FIG. 5, the chamber 41 is vertically oriented and designed tohave a substrate heater 51 positioned axially above the chamber whichwould heat, as by resistance heating, a thin wire or rod 45 ofmolybdenum located centrally, i.e. coaxially, within the chamber. Thesubstrate 45 may have a diameter of about 0.01 inch (0.25 mm) to about0.032 inch (0.8 mm). Surrounding the substrate 45 upon which thedeposition will occur is solid feedstock 43 which may be in the form ofa tube of the desired alloy composition or a plurality of individualrods oriented in a circular array about the central substrate. Thesubstrate heater 51 will heat the single crystal substrate 45 to a hightemperature as described above, e.g. 900° C. to about 1100° C. wherechlorides are being used. The chamber 41 might be surrounded by a usualresistance or induction heater 53 which might be designed and operatedto heat the chamber walls to about 150° C. while heating the feedstockmaterial 43 to a temperature which will generally be at least about 100°C. lower, and preferably at least about 150° C. lower than that of thesubstrate, e.g. feedstock temperatures may be about 700° C. to 900° C.However, higher substrate temperatures may be desirable for reasons setforth hereinafter.

A side entrance 55 is provided in order to initially supply the chamber41 with the desired gaseous atmosphere. Moreover, an exit conduit 57 isalso provided connected via a valve 59 to a pump 61 for evacuating thechamber. Both of these conduits have standard shut-off valves 50, 59.

As an example of operation, the single crystal substrate 45, e.g. Mowire, and the feedstock 43, e.g. W—Ta alloy, are placed within thechamber 41 and the valve 50 closed. Then, the valve 59 leading to theevacuation pump 61 is opened, and the pump operated to evacuate thechamber to an atmospheric pressure of about 1 torr. Once this lowpressure is achieved, the valve 59 is closed, and the valve 50 is openedallowing tungsten chloride vapor to flow into the reaction chamber fromthe heated source, which might be at a temperature between about 80° C.and about 130° C. so that the solid material will have a vapor pressureof about 20 torr. As previously mentioned, a minor amount of hydrogencould be optionally supplied along with the tungsten chloride. When thepressure within the coating chamber reaches about 3-20 torr, the valve50 is closed, and the heaters 51 and 53 are operated to begin the CVD.As the single crystal mandrel 45, e.g. a thin wire of single crystal Mo,and the polycrystalline tungsten and tantalum feedstock 43 are broughtup to operating temperatures, metal alloy from the vaporous chloridesbegins depositing causing the single crystal wire to grow radiallyoutward and creating gaseous Cl₂. The feedstock 43 is heated to anappropriate slightly lower temperature at which a reaction with themetal alloy will occur to form vaporous metal chlorides. RF orresistance heating may be used for either or both heating tasks. Forexample, the temperature of a polycrystalline W/Ta feedstock alloy maybe suitably controlled to provide the desired vaporous atmosphere fromwhich a high density, single crystal body is deposited at the highertemperature of the substrate. WCl₆ and TaCl₅ react at the heatedsubstrate, depositing W and Ta having the desired alloy composition andyielding Cl₂. The Cl₂ diffuses radially outward from the mandrel andtravels to the lower temperature polycrystalline tungsten/tantalumfeedstock 43, where it reacts, producing WCl₆ and TaCl₅.

The operation is allowed to simply continue until the desired diametersingle crystal alloy body has been produced. However, to avoid thepotential build-up of contamination within the chamber 41 as a result ofthe possible presence of minute amounts of contaminants within thefeedstock material, it may be desired to periodically evacuate thechamber to remove any such contaminants. This can be simply done bymomentarily opening the isolation valve 59 and starting the pump 61 toeffect such evacuation; thereafter, that valve 59 is closed and thevalve 50 to the vapor source 48 is momentarily again opened to replenishthe atmosphere as it was initially supplied to start the CVD process.Such evacuation and replenishment might be carried out at any suitableintervals, dependent upon the likelihood of contamination within thefeedstock material, e.g. every 30 minutes or 1 hour.

It has been found that, as the diameter of the resultant body beingcaused to radially grow through CVD substantially exceeds the diameterof the original single crystal wire or rod that serves as the substrate,there is a tendency for the axial orientation of the newly depositedcrystalline material to vary. Generally, this is not a problem until theratio of the diameter of the single crystal body to the diameter of theoriginal substrate exceeds about 3 or 4 to 1. Because this mayoftentimes be the situation, attention has been given to it, and it hasbeen found that carrying out the CVD at a higher temperature, forexample about 1600 to about 2200° C., has the effect of annealing outstrains that may be induced by such alternative crystalline orientationand assures the growth of the single crystal body having the desiredorientation. Accordingly, it may be desirable to employ temperatures inthe higher portion of the range of about 800° C. to about 2200° C.whenever the diameter of the desired resultant product will be more thanabout five times that of the substrate, in order to assure a uniformresultant product. Even when such higher substrate temperatures areemployed, the feedstock temperature is preferably in the range of about700° to about 900° C.

Once a single crystal body of the desired diameter has been achieved,the equipment is shut down and allowed to slowly cool to ambienttemperature. Removal of the body from the chamber 41 and examinationshows that it has indeed achieved single crystal structure with thecrystalline [100] axis aligned longitudinally of the cylindrical body.Measurement also shows that it is fully dense, having achievedessentially 100% of theoretical maximum density for a body made of 93%tungsten and 7% tantalum, with a minute central molybdenum core.

Using this static CVD method, the cost to produce such bodies of highdensity, single-crystal, tungsten alloys particularly suited for use ashigh-density penetrators is reduced significantly over either thetraditional zone-refining method or the standard CVD method. Whenemploying the standard CVD process, for example, a certain proportion ofthe metal chlorides or metal fluorides will not react and will becarried out of the reactor as a part of the exhaust system, which thenmust either be treated to reclaim these reactants or appropriatelydisposed of. Likewise, there are essentially toxic HF, HCl and/or Cl₂vapors that exit the reactor that must be handled in an environmentallyacceptable manner. It can thus be seen that all this adds to the cost ofoperation of the standard CVD process whereas, in the static CVD systemillustrated in FIG. 5, operation is essentially that of a controlledclosed system, and the only waste materials are those which result fromthe momentary evacuations that are carried out.

A single crystal body can also be produced using the CVD systemschematically shown in FIG. 6. In this system, vaporous Cl₂ is suppliedto an upstream reaction chamber 65 wherein a bed of tungsten chips 67are located. Downstream thereof in a separate section 69 of the chamberis a centrally positioned single-crystal substrate 71. A flow of Cl₂into the chip bed is provided which forms tungsten chloride vapor inthis reaction chamber that is heated to a suitable temperature byemploying a suitable tube furnace heater. The tungsten chloride that isformed flows downstream to the CVD chamber 69 via a manifold designed toevenly disperse the gas in a vortex motion. The two-section chamber isvertically oriented, and substrate 71, which may be an electropolishedthin rod of single crystal tungsten (100) located centrally, i.e.coaxially, within the chamber section, is heated by induction heating.The substrate 71 may have a diameter of about 0.1 inch (2.5 mm) and besupported in a graphite holder.

Two side entrance conduits 73 and 75 are provided at the upstream end inorder to supply the chamber with the desired gaseous atmosphere. An exitconduit 77 is connected via a valve 79 to a vacuum pump 81 forevacuating the chamber, and it preferably contains a cold trap 83 and adry trap 85. The gas conduits 73 and 75 are controlled by mass flowcontrollers (MFC) which are calibrated to nitrogen, hence all flowsettings are relative to this calibration.

As an example of operation, the single-crystal substrate 71, e.g. W rod,and the feedstock 77, e.g., W chips, are placed, respectively, withinthe sections 69 and 65 of the chamber. Then, the valve 79 leading to theevacuation pump 81 is opened, and the pump is operated to evacuate thechamber to a pressure of about 0.8 torr.

The induction heater is controlled to heat the single-crystal tungstensubstrate to a temperature of about 1750° C., and the tube furnace thatsurrounds the upstream section of the reactor is used to heat the bed oftungsten chips to a temperature of about 900° C. A purge flow ofhydrogen is supplied through the side conduit 73 at a setting of about200, i.e. a setting calibrated at 200 standard cubic centimeters perminute (sccm) of nitrogen, and the purge at this temperature iscontinued for about two hours. The hydrogen MFC is then closed in theside conduit 73, and the substrate is cooled to ambient. The reactionchamber is pumped out by the vacuum pump so as to remove substantiallyall of the hydrogen while the feedstock bed is maintained at about 900°C. The mandrel is then heated to about 1750° C., while graduallybringing the flow of chlorine gas through the conduit 75 to a setting of100. The 2-section chamber is maintained at a pressure of about 0.95torr by controlling the valve 79.

The chlorine setting and this pressure are maintained for about 2 hours,during which time the temperature of the mandrel is slowly raised of toabout 1800° C.; then the flow of chlorine gas is gradually increased toa setting of about 125, and the temperature raised to about 1850° C.Both are then so maintained during the second two hour period. At theend of this second two hour period, the chlorine setting is raised toabout 150, and the mandrel temperature is raised slowly to about 1900°C. via the induction heater. Both are so maintained for the remainder ofabout 3 hours. At the end of this three hour period, with the mandrel atabout 1900° C., the flow of chlorine is raised to a setting of about175, and such conditions are maintained for about 4 hours. At the end ofthis 11 hour coating run, the flow of chlorine is halted, and thetemperature of the mandrel is cooled to about 750° C. over just abouttwo minutes time, where it is maintained for about 1 minute before allpower to the induction heater is turned off. Power is also removed fromthe tube furnace, and the bed of tungsten chips is allowed to cool toambient. The system is then flushed overnight through a liquid KOHscrubber (not shown) with helium supplied through side conduit 75.

The diameter of the body fairly radially grows through CVD and fairlyquickly substantially exceeds the diameter of the original singlecrystal rod that serves as the substrate. After about 11 hours, thesingle crystal substrate has grown to about a diameter of 0.3 in (7.6mm), thus exceeding the diameter of the original substrate by over 300%.

Removal of the tungsten body from the chamber 69 and examination showsthat it has indeed achieved single-crystal structure with thecrystalline [100] axis aligned longitudinally of the cylindrical body.Analysis also shows that it is fully dense, having achieved essentially100% of theoretical maximum density for a body made of 100% tungsten.

In certain instances, it may be desirable to have the penetrator includesome pyrophoric material, i.e. a pyrophor, which will oxidize and createsmoke or fumes that will be indicative that a particular target hasindeed been penetrated by breaching its armor, thereby allowing focus tobe shifted to another potential target. Suitable pyrophoric materialsfor this purpose include hafnium, titanium and zirconium. In the case ofan otherwise homogenous penetrator, it might be suitable to simply drillout the original molybdenum core and then fill this core with a suitablepyrophor, e.g. hafnium. On the other hand, if a multiple rod penetrator,such as that depicted in FIG. 3, is employed, one or more small rods ofhafnium or another pyrophor could be included or discrete particles of apyrophor might be included as a part of the matrix WHA material used tocombine the plurality of single crystal tungsten rods into such acomposite penetrator 21.

Although the invention has been described with regard to certainpreferred embodiments which constitute the best mode presently known tothe inventor, it should be understood that various changes andmodifications as would be obvious to one having the ordinary skill inthis art, may be made without departing from the invention which isdefined by the claims appended hereto. For example, although thediscussion of the fabrication processes mention using a feedstock of 93%tungsten and 7% tantalum, all or a part of the tantalum might besubstituted by rhenium, and rhenium chloride (ReCl₄ or ReCl₆) in a minoramount might be included with the vaporous WCl₆ that is supplied to thechamber. Likewise, in a conventional CVD process, a mixture of hydrogen,tungsten fluoride and rhenium fluorides might be used, or alternativelyall or some of the alloying metal could be supplied by niobium fluoride,while still creating a single crystal tungsten alloy penetrator havingits [100] axis oriented in the desired direction.

Particular features of the invention are emphasized in the claims whichfollow.

1. A method for making a single-crystal, high density body containing atleast about 90 weight % of tungsten, said method comprising: providing achamber suitable for carrying out chemical vapor deposition (CVD),locating a stable single-crystal substrate within said chamber,providing a vapor atmosphere containing chlorides or fluorides oftungsten in said CVD chamber, and heating said single-crystal substrateto a temperature between 1600° C. and 2200° C. so as to cause asingle-crystal tungsten body to grow upon the exterior surface of saidsingle-crystal substrate and create a high-density tungsten body.
 2. Themethod according to claim 1 wherein said substrate is a thin wire whichis aligned with the [100] orientation with respect to its long axis. 3.The method according to claim 2 wherein said single-crystal substrate isformed of a metal or an alloy of metals having a body-centered cubiccrystal structure.
 4. The method according to claim 3 wherein saidsubstrate is molybdenum, tungsten, niobium or tantalum, or an alloythereof.
 5. The method according to claim 1 wherein said heating iscontinued until said single-crystal body has grown to have a diameter ofat least about 3 mm.
 6. The method according to claim 1 wherein saidvapor atmosphere contains a minor amount of chlorides or fluorides oftantalum, rhenium, niobium and/or molybdenum and wherein said singlecrystal tungsten body is an alloy of tungsten and tantalum, rhenium,niobium and/or molybdenum.
 7. An economical method for making asingle-crystal, high density body containing a major amount of tungsten,said method comprising: providing a chamber suitable for carrying outchemical vapor deposition (CVD) which can be periodically closed tooutlet flow therefrom, locating a stable, single-crystal substratewithin said chamber, providing a solid feedstock in the form of a majoramount of elemental tungsten in said CVD chamber, heating said substrateto at least about 800° C. and heating said solid feedstock to atemperature of at least about 700° C. but below that of said substrate,and initially introducing vapor into said chamber containing chlorine orfluorine and then discontinuing vapor flow into or out of said chamberto cause the deposition of a single-crystal tungsten body upon saidsubstrate with the simultaneous creation of Cl₂ or F₂ vapor which reactswith said heated solid feedstock to form metal halide vapors that thenreact at said substrate.
 8. The method according to claim 7 wherein saidchamber is periodically evacuated and the atmosphere of said evacuatedchamber is resupplied with said vapor initially introduced.
 9. Themethod according to claim 7 wherein said vapor contains chlorine,wherein said single-crystal substrate and said growing single-crystalbody are heated to a temperature between about 1600° C. and about 2200°C., and wherein said feedstock is heated to a temperature which is notabove about 900° C.
 10. The method according to claim 7 wherein saidvapor contains tungsten fluoride and hydrogen, causing the deposition ofelemental tungsten upon said substrate with the simultaneous creation ofHF, which HF subsequently reacts with said heated solid feedstock toform additional metal vapors.
 11. The method according to claim 7wherein said substrate is a thin wire which is aligned with the [100]orientation with respect to its long axis.
 12. The method according toclaim 11 wherein said single-crystal substrate is formed of a metal oran alloy of metals having a body-centered cubic crystal structure. 13.The method according to claim 7 wherein said heating is continued untilsaid single-crystal body has grown to have a diameter of at least about3 mm.
 14. The method according to claim 7 wherein said feedstockcontains a minor amount of tantalum, rhenium, niobium and/or molybdenumas an alloying metal and wherein said single crystal tungsten body is analloy of tungsten and a minor amount of said elemental alloying metal ormetals.
 15. A method for making a single-crystal, high density bodycontaining a major amount of tungsten, said method comprising: providinga chamber suitable for carrying out chemical vapor deposition (CVD),locating a stable, single-crystal substrate within said chamber,providing a solid feedstock in said chamber in the form of a majoramount of elemental tungsten at a location upstream of said substrate,heating said substrate to at least about 800° C. and heating said solidfeedstock to a temperature of at least about 700° C. but below that ofsaid substrate, and causing chlorine or fluorine vapor to flow into andthrough said chamber to cause an initial reaction with said heated solidfeedstock to form metal halide vapors that then react at said substrateto effect deposition of a single-crystal tungsten body upon saidsubstrate.
 16. The method according to claim 15 wherein said vaporcontains chlorine, wherein said single-crystal substrate and saidgrowing single crystal body are heated to a temperature between about1600° C. and about 2200° C., and wherein said feedstock is heated to atemperature which is not above about 900° C.
 17. The method according toclaim 15 wherein said substrate is a thin wire which is aligned with the[100] orientation with respect to its long axis.
 18. The methodaccording to claim 17 wherein said single-crystal substrate is formed ofa metal or an alloy of metals having a body-centered cubic crystalstructure.
 19. The method according to claim 15 wherein said heating iscontinued until said single-crystal body has grown to have a diameter ofat least about 3 mm.
 20. The method according to claim 15 wherein saidfeedstock contains a minor amount of tantalum, rhenium, niobium and/ormolybdenum as an alloying metal and wherein said single crystal tungstenbody is an alloy of tungsten and said elemental alloying metal ormetals.